1. Field of the Invention
The present invention relates to a connecting structure for piping members used for fluid transportation in various industries such as chemical, semiconductor, food, biochemistry, in particularly to a connecting structure for piping members being easy to connect and capable of maintaining good sealing performance over prolonged period.
2. Description of the Related Art
In conventional connecting structures integrating valve portions therein for use in various chemical lines and pure-water lines, connection has been made by using fittings integrated into a piping member such as valves and tubes between piping members. However, there have been problems in that the piping work for such a configuration is time-consuming and requires wider piping space.
As a means of solving the problems a manifold valve 101 integrating the valve portions shown in FIG. 9 has been used. The manifold valve 101 includes a main channel 102 provided inside the valve body 103, multiple communicating ports 104 vertical to the main channel 102, multiple valve chests opening upward in communication with the communicating ports 104, valve seats 106 located in place where the lower side of the valve chest 105 intersects the communicating port 104, and sub-channels (not shown) provided in the sides of the valve chests 105 in orthogonal direction with respect to the main channel 102 and the communicating port 104. Multiple driving sections 108 provided with the valve bodies 107 serve to open and close the valves utilizing the pressure of the working fluid and are fixed on the top of the valve body 103 with bolts and nuts (not shown) in relation to the respective valve chests 105. This forms a structure with multiple integrated valves. However, the manifold valve 101 is inferior in versatility, because its design and manufacture has to be adjusted to each particular requirements, i.e., increasing or decreasing the number of valve chests 105 and sub-channels. If the valve seat 106 is damaged even partly by accidental inclusions or similar events, requiring replacement of parts, the entire valve body 103 as well as the not affected parts have to be replaced, because of the integrated structure of the valve body 103. This poses problems because of the required extensive labor and high costs.
As means of solving the aforementioned problems, connecting structures of connecting openings of blocks, as shown in FIG. 10 has been proposed (refer to Japanese Unexamined Patent Application Publication No. 2001-116155). According to this connecting structure, a first connecting surface 109 is closely connected to a second connecting surface 110. An annular recess groove 111 is formed in the first connecting surface 109 and an annular projection 112 projects from the second connecting surface 110. On the periphery of the annular projection 112 an annular projection 115 with a head 113 and a tapered surface 114 are formed (refer to FIG. 10(a)). When the connecting surfaces are secured with securing members (not shown) such as bolts, the annular projection 112 is brought into close contact with the periphery of the opening and the annular projection 115 is fitted into the annular recess groove 111, while the tapered surface 114 of the annular projection 115 is brought into close contact with the inner periphery of the annular recess groove 111 (refer to FIG. 10 (b)).
In this connecting method, however, the connected portions consisting of the annular projection 112, the annular projection 115, and the annular recess groove 111 are kept tight at first because they are secured sufficiently with a securing member (not shown) such as a bolt and others. Yet, this does not address the problem that sealing performance deteriorates due to weakened crimping forces of the connected portion resulting from creep action caused by changes in fluid pressure and temperature over prolonged periods, thus rendering connected parts susceptible to separation due to looseness developing in securing members, resulting in leakage of fluid. The tendency becomes more pronounced with polytetrafluoroethylene (hereinafter referred to as PTFE) and tetrafluoroethylene perfluoroalkyl vinylether copolymer (hereinafter referred to as PFA) preferably used as sealing materials.